1. Technical Field
The present invention relates to optical instruments and more particularly, to optical instruments that are used for imaging and have an ultra wide band operation range.
2. Discussion of the Related Art
Optical instruments with an ultra wide band have many applications. For example, imaging devices such as cameras that may be effectively operable within a wide range of lighting conditions. One exemplary non-limiting application is a camera in use with airplanes configured to capture a video of the landing lights along runways. Such a camera needs to be able to be fully operable in daylight conditions but also in harsh weather conditions. Consequently, it has to operate both in the visible light range with a wavelength spanning from 0.35 μm to 0.7 μm but also along the Infra Red (IR) range spanning from 0.7 μm to 4 μm and beyond.
Ultra wide band imaging sensors in the 0.4 μm-5 μm are being developed but are difficult to accommodate with suitable optical arrangements. Due to their properties they impose strict optical and mechanical design requirements on the optical arrangements that accompany them. For example, in order to meet specified design requirements of field of view and resolution, a specified back focal length is required. The back focal length requirement is sometimes difficult to address due to the fact that optical instruments that are operable within the IR range require certain modules that need to be located between the optical arrangement and the imaging sensor. Such modules, such as a cold shield and a shutter have minimal dimensions that may extend well beyond the required back focal length of the optical arrangement.
Other constraints due to the wide spectral band of the aforementioned requirements necessitate a use of a plurality of sensors (each covering a different spectral range) and also relate to different heat radiation absorption mechanism of IR sensors.
Mirror based solutions for the aforementioned design challenges are known in the art. However, there are no lens-based optical arrangements that are known to address the strict optical and dimensional limitations imposed by ultra wide bend optical sensors.